Cathode ray tube

Details Cathode ray tube Cathode ray tube

2003-05-05

2004-09-14

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With electrical shield or static charge distribution means

C315S008000, C315S085000

Reexamination Certificate

active

06791249

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube that uses a degaussing coil for demagnetizing metal parts in the cathode ray tube such as a color selection apparatus and an inner shield.
2. Related Art
Metal parts are typically found in a cathode ray tube (CRT). Such metal parts include (a) a color selection apparatus comprised of a shadow mask that has a plurality of apertures for performing color separation of three electron beams, which are emitted from an electron gun, to corresponding red, green, blue (R,G,B) phosphors of a phosphor screen, and a mask frame for fixedly supporting the shadow mask at a predetermined location in the cathode ray tube (CRT); and (b) an inner shield for shielding from the earth's magnetic field a path through which the electron beams travel.
However, the metal parts nevertheless become magnetized by the earth's magnetic field so that a magnetic field is formed in the peripheries of the metal parts. Such a magnetic field changes the paths through which the electron beams travel such that the intended phosphors are not illuminated by the electron beams. That is, mis-landing of the electrons beams occurs, and this reduces picture quality.
To remedy this problem, a degaussing coil is mounted on an outer circumference of a funnel of the cathode ray tube (CRT). The degaussing coil operates for a period of three to four seconds each time the cathode ray tube (CRT) is turned on, during which time a degaussing current is used to demagnetize the color selection apparatus and the inner shield.
Examples of degaussing coil technology include a magnetic treatment method disclosed in Japanese Laid-Open Patent No. Heisei 8-306316 by Yoshida, published on Nov. 22, 1996, and an automatic demagnetizing circuit for a cathode ray tube (CRT) disclosed in Japanese Laid-Open Patent No. Heisei 9-13 5451 by Ikeda et al., published on May 20, 1997.
When using a degaussing coil for a cathode ray tube (CRT), it is essential that an initial current value of a power supplied to the degaussing coil is optimized so that the magnetization state of the metal elements maybe removed in a short interval and so that satisfactory restoration to a demagnetized state may be realized. However, with the art described above, no such specific disclosure of an optimal initial current value is provided. Accordingly, quick and sufficient demagnetization is not possible, thereby making actual application impractical.
SUMMARY OF THE INVENTION
The present invention provides a cathode ray tube capable of realizing demagnetization of metal parts of the cathode ray tube in a short period of time.
The present invention provides a cathode ray tube that improves the ability to restore metal parts to a demagnetized state.
In one embodiment, the present invention provides a cathode ray tube that includes an evacuated envelope including a face panel, a funnel, and a neck; a color selection apparatus mounted inwardly from the face panel; an electron gun mounted within the neck; a magnetic shield mounted connected to the color selection apparatus; and degaussing coils mounted to an outer surface of the evacuated envelope. A degaussing current flowing to the degaussing coils has a waveform such that a line connecting a peak A from where a maximum current value first starts to decrease and a peak G of a sixth cycle is a functional curve of a second degree or greater. And in this interval, the peak values are gradually decreased. That is, the first differential value of a function of the line connecting from peak A to peak G to time does not have zero.
If the maximum current value is I
p-p
, a current value of a third cycle is I
3
, and a current value of the sixth cycle is I
6
, the following Equations 1 and 2 are satisfied,
I
3
/[(
I
p-p
+I
6
)/2]>1.0  (Equation 1)
(
I
6
/I
p-p
)≧0.89  (Equation 2)
In another embodiment, the present invention provides a cathode ray tube that includes an evacuated envelope including a face panel, a funnel, and a neck; a color selection apparatus mounted inwardly from the face panel; an electron gun mounted within the neck; a magnetic shield mounted connected to the color selection apparatus; and degaussing coils mounted to an outer surface of the evacuated envelope. A degaussing current flowing to the degaussing coils has a waveform such that a line connecting a peak A from where a maximum current value first starts to decrease and a peak F of a fifth cycle is a functional curve of a second degree or greater.
If a line connecting the peak A to a point H where the functional curve changes direction is AH, a line connecting the peak F to a point I on line AH where a line drawn through the peak F perpendicularly intersects the line AH is FI, a length of line AI connecting the peak A to point I is L
1
, and a length of line FI is L
2
, the lengths L
1
and L
2
satisfy the following Equation 3, and if a maximum inrush current is I
p-p
and a current of the fifth cycle is I
5
, the following Equation 4 is satisfied,
(
L
1
/L
2
)<3.0  (Equation 3)
(
I
5
/I
p-p
)≧0.9  (Equation 4)
The degaussing current is damped by a right temperature characteristic thermistor.
The color selection apparatus includes a mask frame having support members provided at predetermined spacings, and a pair of elastic members, each of which is connected to the support members extending from one support member to an opposing support member; and a mask having a plurality of apertures for the passage of electron beams, the mask being connected to the supported members in a state receiving tension.
The degaussing coils include a first degaussing coil and a second degaussing coil mounted at opposing positions about the electron gun, the first degaussing coil and the second degaussing coil being connected in series.
In accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a cathode ray tube, comprising: an evacuated envelope including a face panel, a funnel, and a neck; a color selection apparatus being adjacent to the face panel; an electron gun being mounted within the neck; a magnetic shield being mounted to said color selection apparatus; and degaussing coils being mounted to an outer surface of said evacuated envelope, with a degaussing current flowing to said degaussing coils, the degaussing current having a waveform with a line connecting a peak A and a peak G, the peak A corresponding to a point where a maximum current value first starts to decrease, the peak G corresponding to a peak of a sixth cycle, the line corresponding to a functional curve, the functional curve corresponding to one curve selected from a curve of second degree and a curve of a greater degree than second degree.
In accordance with the principles of the present invention, as embodied and broadly described, the present invention provides a cathode ray tube, comprising: an evacuated envelope including a face panel, a funnel, and a neck; a color selection apparatus being adjacent to the face panel; an electron gun being mounted within the neck; a magnetic shield being mounted to said color selection apparatus; and degaussing coils being mounted to an outer surface of said evacuated envelope, with a degaussing current flowing to said degaussing coils, the degaussing current having a waveform with a line AF connecting a peak A and a peak F, the peak A corresponding to a point where a maximum current value first starts to decrease, the peak F corresponding to a peak of a fifth cycle, the line AF corresponding to a functional curve, the functional curve corresponding to one curve selected from a curve of second degree and a curve of a greater degree than second degree.
In accordance with the principles of the present invention, as embodied and broadly described, the present invention provides an apparatus, comprising: at least one degaussing coil being mounted to an outer surface of an evacuated envel

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